How do I go about cashing a check made out to my mother's estate if there was no estate checking account set up?

This life insurance had my stepfather as beneficiary but he predeceased my mother by 18 months. Shortly before she died, my mother told my sibling and I she wanted me to have this money. My brother is the executor but there was very little to the estate so he never set up an estate account. We handled everything between us. How can I get this Check deposited without opening an estate account?